With that done all that remains is for you to switch between the two keyboards. You do this using this button:

Doing that for the first time brings up this notification:

Then you get the keyboard ... and it's pretty cool!

There are a load of emoticons to choose from (click here to see them all). You can use these all over the place, but remember that they'll only display properly on iOS devices, so if you use them in say the Twitter app, only other iOS users will be able to see them properly, so use them with care!